SOPD SCADA Systems 2 — Questions and Answers
Question 1: What is the primary function of a Remote Terminal Unit (RTU) in a SCADA system?
- Process operator commands at the control center
- Collect field data and transmit it to the master station (Correct answer)
- Store historical data for trending analysis
- Manage network communication protocols
Correct answer: Collect field data and transmit it to the master station
RTUs collect analog and digital data from field devices and transmit it to the SCADA master station for monitoring and control.
Question 2: In SCADA communications, what does the term 'polling' refer to?
- A method where the master station periodically queries each RTU for data (Correct answer)
- A technique for encrypting data transmissions
- A process for validating RTU firmware
- A backup communication path activation procedure
Correct answer: A method where the master station periodically queries each RTU for data
Polling is a master-initiated communication method where the control center sequentially queries each RTU to retrieve current status and measurements.
Question 3: Which SCADA display element is used to show the real-time state of a circuit breaker as open or closed?
- Trend chart
- Status point (digital point) (Correct answer)
- Analog meter display
- Alarm summary table
Correct answer: Status point (digital point)
Status points (digital points) represent two-state or multi-state equipment conditions such as breaker open/closed positions on SCADA displays.
Question 4: What distinguishes a Supervisory Control and Data Acquisition (SCADA) system from a Distributed Control System (DCS)?
- SCADA systems operate at higher voltages than DCS
- SCADA is designed for geographically dispersed sites while DCS manages localized continuous processes (Correct answer)
- DCS systems use satellite communication while SCADA uses fiber
- SCADA cannot perform automatic control actions unlike DCS
Correct answer: SCADA is designed for geographically dispersed sites while DCS manages localized continuous processes
SCADA systems are optimized for monitoring and controlling assets spread over large geographic areas, whereas DCS systems focus on continuous process control within a single facility.
Question 5: When a SCADA system shows a 'stale' data indication, what does this mean for the operator?
- The data value is outside its normal operating range
- The RTU is reporting a measurement error
- The data has not been updated within the expected scan interval (Correct answer)
- The communication channel has switched to backup path
Correct answer: The data has not been updated within the expected scan interval
Stale data indicates that the SCADA master has not received a fresh update from the RTU within the configured scan cycle, suggesting a communication or RTU issue.
Question 6: Which protocol is most commonly used for SCADA communication in North American electric utility systems?
- Modbus RTU
- DNP3 (Distributed Network Protocol 3) (Correct answer)
- IEC 60870-5-101
- PROFIBUS
Correct answer: DNP3 (Distributed Network Protocol 3)
DNP3 is the dominant SCADA communication protocol in North American electric utilities due to its reliability, time-stamping capability, and support for unsolicited reporting.
Question 7: What is the purpose of the 'tag database' in a SCADA system?
- Store alarm history for regulatory reporting
- Map communication addresses to human-readable point names and engineering units (Correct answer)
- Track operator login sessions and actions
- Archive raw communications for cybersecurity auditing
Correct answer: Map communication addresses to human-readable point names and engineering units
The tag database associates RTU register addresses with descriptive point names, scaling factors, and engineering units so raw data can be displayed meaningfully to operators.
SOPD SCADA Systems 2
What is the primary function of a Remote Terminal Unit (RTU) in a SCADA system?